1. Field of the Invention
The present invention relates to an apparatus for generating and manipulating a high-pressure fluid jet, and more particularly, to an apparatus for generating a high-pressure waterjet and manipulating it about multiple axes.
2. Description of the Related Art
High-pressure fluid jets, including high-pressure abrasive waterjets, are used to cut a wide variety of materials in many different industries. Systems for generating high-pressure abrasive waterjets are currently available, for example the Paser 3 system manufactured by Flow International Corporation, the assignee of the present invention. An abrasivejet cutting system of this type is shown and described in Flow's U.S. Pat. No. 5,643,058, which patent is incorporated herein by reference. In such systems, high-pressure fluid, typically water, flows through an orifice in a cutting head to form a high-pressure jet, into which abrasive particles are entrained as the jet flows through a mixing tube. The high-pressure abrasive waterjet is discharged from the mixing tube and directed toward a workpiece to cut the workpiece along a selected path.
Various systems are currently available to move a high-pressure fluid jet along a selected path. (The terms “high-pressure fluid jet” and “jet” used throughout should be understood to incorporate all types of high-pressure fluid jets, including but not limited to, high-pressure waterjets and high-pressure abrasive waterjets.) Such systems are commonly referred to as two-axis, three-axis and five-axis machines. Conventional three-axis machines mount the cutting head assembly on a ram that imparts vertical motion along a Z-axis, namely toward and away from the workpiece. The ram, in turn, is mounted to a bridge via a carriage, the carriage being free to move parallel to a longitudinal axis of the bridge in a horizontal plane. The bridge is slideably mounted on one or more rails to move in a direction perpendicular to the longitudinal axis of the bridge. In this manner, the high-pressure fluid jet generated by the cutting head assembly is moved along a desired path in an X-Y plane, and is raised and lowered relative to the workpiece, as may be desired. Conventional five-axis machines work in a similar manner but provide for movement about two additional rotary axes, typically about one horizontal axis and one vertical axis.
Manipulating a jet about five axes may be useful for a variety of reasons, for example, to cut a three-dimensional shape. Such manipulation may also be desired to correct for cutting characteristics of the jet or for the characteristics of the cutting result. More particularly, as understood by one of ordinary skill in the art, a cut produced by a jet, such as an abrasive waterjet, has characteristics that differ from cuts produced by more traditional machining processes. Two of the cut characteristics that may result from use of a high-pressure fluid jet are referred to as taper and trailback. Taper refers to the relative angle of a plane of the cut wall to a plane formed by the vectors of the jet and the direction of traverse. Trailback, also referred to as drag, identifies the phenomena that the fluid jet exits the workpiece at a point behind the point of entry of the jet into the workpiece, relative to the direction of travel. These two cut characteristics, namely taper and trailback, manifest themselves in geometrical anomalies that may or may not be acceptable, given the desired end product. Taper is typically not acceptable and requires an additional machining process to straighten the walls of the cut. Trailback effects cutting around corners and curves, the lag resulting in undesirable undercutting at the bottom (jet exit) side of the cut. In situations where it is desirable to minimize or eliminate taper and trailback, conventional 3D-cutting systems have been used with substantially reduced travel rates, primarily through trial and error, to allow the jet spreading characteristics to favorably alter the geometry of the cut. As this process is typically done by manual trial and error, it is time consuming and often unsuccessful.
Applicants believe it is desirable and possible to provide an improved system for generating and manipulating a high-speed fluid jet, for motion along one or more axes. The present invention provides such a system.